在C ++中删除指针 [英] Delete pointer in c++

问题描述

嗨！我也有删除poiter的问题.
这是我的代码.

  int  main()
{
    向量< int *>列表;
     int  * a;
     for ( int  i =  0 ; i< ; 10; i ++)
    {
        a = 新  int ();
        * a = i;
        list.push_back(a);
    }
     int  * value = 新  int () ;
    * value =  4 ;
    list.push_back(值);
    cout<< " << * value<< endl;
    /*  删除指针，减去5 */
     for ( int  i =  0 ; i< ; list.size(); i ++)
    {
        如果(* list [i]< 5)
        {
            删除列表[i];
            list [i] = NULL;
        }
    }
    如果(值！= NULL)
        cout<< " << * value<< endl;
    其他
        cout<< " << endl;
} 

我认为value必须为NULL，但不是Null，因此删除后如何将其为NULL！

解决方案

在这些行之间:

  int  * value = 新  int ();
* value =  4 ;
list.push_back(值);
cout<< " << * value<< endl;  



这行:



if(value!=NULL)
 



您对名称为value的变量完全不执行.您认为通过什么魔术可以将其设置为NULL?

//那么删除后如何将其设置为NULL?

请尝试进行小的修改:):

 vector< int *&> list; 

所有其他解决方案都是有效的，但是还需要注意的是，当您在分配的变量上调用delete时，指针不会自动变为NULL值.即使释放了变量，指针本身也将保留该值.如果要使指针变为NULL，则必须手动设置它.

int *value = new int; //allocate memory on the heap
delete value;         //value STILL contains a pointer, but it''s no longer valid
value = NULL;         //Now the pointer has been reset

Hi! I have same problem with delete poiter.
This''s my Code.

int main()
{
    vector<int*> list;
    int *a;
    for(int i=0;i<10;i++)
    {
        a=new int();
        *a=i;
        list.push_back(a);
    }
    int *value=new int();
    *value=4;
    list.push_back(value);
    cout<<"value : "<<*value<<endl;
    /*Delete pointer less 5*/
    for(int i=0;i<list.size();i++)
    {
        if(*list[i]<5)
        {
            delete list[i];
            list[i]=NULL;
        }
    }
    if(value!=NULL)
        cout<<"value : "<<*value<<endl;
    else
        cout<<"It's NUll"<<endl;
}

I think value must NULL but It''s Not Null, so how do it NULL when it''s deleted!

解决方案

Between these lines:

int *value=new int();
*value=4;
list.push_back(value);
cout<<"value : "<<*value<<endl;

and this line:

if(value!=NULL)

You do absolutely nothing to the variable named value. By what magic do you think it will get set to NULL?

// so how do it NULL when it''s deleted ?

Please try the small modification :) :

vector<int*&> list;

All the other solutions are valid, but it''s also important to note that when you call delete on an allocated variable, the pointer will NOT automatically turn into a NULL value. The pointer itself will keep the value even if the variable is deallocated. If you want the pointer to become NULL, you have to manually set it.

int *value = new int; //allocate memory on the heap
delete value;         //value STILL contains a pointer, but it''s no longer valid
value = NULL;         //Now the pointer has been reset

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